Empty out your prefs.prop file:
- Find the prefs.prop file. It may be under "Documents\Telltale Games\Jurassic Park the Game" if you're using Windows 7. For XP, I believe the file is under "My Documents\Telltale Games\Jurassic Park the Game". You could also just search your install drive, it will be in a Telltale Games folder somewhere.
- Open it up in notepad and delete everything inside
- Save and close
Then try starting the game.